Note: Descriptions are shown in the official language in which they were submitted.
11360~
C PO1 BACKGROUND OF q~IE I~VENTION
~77 The present invention relates to ~me~al~ coating
particularly for plastic and other dielectric articles
Electroless or autocatalytic deposition of metallic
coatings on non-c~nductive or dielectric surfaces, such as
,. .. .
plastics, is a well known procecs with broad applications in
diversified industries such as automotive, radio, televisi~n,
plumbing, marine, home appliance, etc~ However, for the benefit
of clarity to the non-artisan, it is stated here electxoless
plating which is the subject of this invention and referred to
frequently throughout this disclosure requires no electricity
for metallic deposition while electroplating or electrodeposi- -
tion requires its employment. The field is generally described
in my book, "Metallization of Plastics" ~Reinhold, ~ew YorX
,.:, - . . -
~,5 1960), see also the U.S~ patents cited below.
Heretof~re, the application of the electroless
coating to surfaces of substratesl following pretreatment of
said surfacesl was followed by the commonly used electr~plating
or electrodeposition process kno~7n to the industry particularly
0 electroplated copper, nickel, chromium, gold, silver, etc. to
achieve bright surfaces for decorative or functional purposes,
These prior art processes involve chemical etching of the
plastic substrate mainly to improve adherence of metal thereto~
then sensitizing and activating this etched surface, applying
.
~5 a conductive film of silver, copper or nickel and electro-
- plating of the desired metal upon this conductive film.
Recent improvements have eliminated the two-step
treatment [i~e. 1 - sensitizing and 2 - activating] and re-
placed it with a one-step pretreatment involving colloidal
O solutions containing non-noble copper ions or noble palladium
ions; then a conductive film of ccpper or nickel is formed
and, finally, electroplating metal is applied.
-2-
,
"' ~ 1S36006
C P01 As an ~xample of the non-noble catalyst treatment
1/77 referred to, the U.S. Patent *4,020,197 issued to Steffen
~Apxil 26, 1977) treats the plastic surface in a solution of
cuprous chloride, acidifiea ~ith 10-15% hydrochloric aci~,
followed by hydrolysis of the cuprous (1) compound to a
hydrous oxide in hot water; th~n acceleration in an alkaline
solution of sodium borohydride. Innumerable patents issued
to Feldstein such as u.S~ Patents ~3,993,799, ~3,993,848,
~3,993,801, ~3,993,491, ~3,993,799 and ~3,982,054 also
0 practice the employment of the so-called non-noble ~etal -
catalyst for treat~ent of non-conductive surfaces.
As an example of the noble catalyst referred to, a
patent was issued to Shipley, U.S. Patent ~3,011,920
~December 5, 1961) in which the no~ 1 metal, e.g,, palladium, is
applied directly to the die'ectric surface in the form of a
colloidal solution containing the metal in ~ero valence state.
; Normally, the metal is formed in the colloidal solution by intro-
ducing both palladium chloride and stannous chloride into a
highly acidified (with hydrochloric acid) aqueous solu~io~, the - ',
palladium ions being reduced within the solution to this ze~o
valence state by the stannous ions. U.S. Patent ~3,672,938
issued June 27, 1972, to ZeblisXy and ~3,767,583 issuea
October 23, 1973, to Fadgen and Sau~estre also practice the use
of the noble catalyst solution.
Processes of the above nature involvin~ pretreatment
and formation of a conductive film of copper or nickel for
making the plastic conductive followed by electroplating have
been commercially successful but have many technical ana
economic disadvantages.
From a technical point of view, intricate parts with
blind-holes, threads, small diameter holes, slots, recesses or
internal areas do not receive uniform electroplating because,
-3-
-
6()06
~r
r
~C POl by nature, c~rtain placiny baths have poor throwing po~er; for
1/77 example, as in the case o~ chromium plating, and costly
au~iliary anode assemblies, commonly employed in the industry
must be used to plate into these extremely low current density
' ~ 5 areas. Excessive plated metal occurs on the high current
density areas, such as sharp corners, protrusions, etc., while
little or even no plating takes place in the low current
density areas such as grooves, holes, slots, etc. In other
words, uneven thickness of electrodeposits result due to the
~ 10 fact that the high current density araas receive more metal
,~ than the low current densit~ areas.
Economically, the cost ~or applying an electroplated
coating to the plastic is much greater because of the relative?y
thick deposits applied to the conductive film of copper or -
nickel. Excessive metal costs are incurred. - -
Furthermore, plastic parts, especially those large
in size, re~uire placement on plating racks for acceptable
electroplating rêsults~ Fixture costs and labor for attaching
the parts to said fixture bring about these additional process
expenditures. Furthermore, unplated contact points appear `
r where the parts are held on these fixtures ~hich is highly
~bjectionab~e in critical industrial applications.
There is a need for electroless plating compositions
and processes producing bright deposits especially in the decora-
tion of plastics which will overcome the aforementioned aiS - ~
advantages while still being cc~patible with known commercial
procedures. The present invention provides said compositions
and processes. -
While the application of bright electroless ~ r ^
deposits, applied in bulk or mass handling, or with rack
handl.ng, is common practice when these deposits are applied
to non-ferrous or ferrous substrates, the brightness can only '~
.,
60C6
~' P02 ¦~be achieved by bright-dipping or polishing the metal substrate
~177 Ijfirst to obtain these bright electroless finishes. Non-conductive
` I surfacesare normally impossible to bright dip and polishing of
non-conductive surfaces is not feasible since there would be a
loss of adhesion of the electroless coating to the non-conductive
¦surface due to the absence of mechanical or chemical interlocking
of the metallic coating.
; It is the principal object of the present invention
to provide an effective and economical process for electrolessly
~0 =, applying attractive, bright metallic coatings to non-conductive
surfaces, particuLarly a wide variety of synthetic resins, for
~ ~ ~ex~ple, acrylonitrile-butadiene-styrene (ABS), without the
; necessity of subsequent electroplating.
It is a further particular object of the present
L5 ~ ¦~invention to provide a process whereby pIastic parts, no matter
~howlintricate in shape, form, or de-sign, can receive a bright
electroless coating uniformly deposited throughout the entire
part without~using costly racking and auxiliary anode assemblies
~ to insure this uniform metal thickness in both high and low
~ ¦current density areas. In other words, the object is to provide
a process wherein parts may be processed in bulk or in mass
I wlthout~the necessity of racking and still receive bright
deposits of electroless metal with complete elimination of the
need for electroplated deposits and reIated burdens of process
and equipment.
SUM~RY OF THE INVENTION
The process of the present invention is applicable
to the metallic coating, with a selected metal, of a wide
ariety of dielectric substrates but is best employed commercially
to apply bright metallic coatings to plastics such as acryloni-
trile-butadiene styrene (ABS). Other non-conductive substrates
escribed in the prior art, including the broad range of thermo- i
,.,, ~ ,,. ~
5-
~: :~' I
,. I
` -
i13~
plastic and thermosetting resins, glass, ceramics, etc., may
be suitably electrolessly coated,with the desired metal
with the present invention. In practice, these substrates
are surface conditioned or etched in the manner known to the
artisan prior to the electroless process in order to improve
the adherence of the metallic underlayer. The etched substrate
is then sensitized and activated in a one-stage or two-stage
process (preferably one-stage) utilizing the noble or non-noble
activator or catalyst previously discussed. The pretreated
substrate i-s then coated with electroless copper, termed in
this invention, the primary electroless coating (underlayer),
applied from a special composition to produce a dense, levelled
electroless copper deposited in proper thickness to act as a
suitable foundation metal for receiving the secondary electro-
less metal possessing attractive brightness. This combination
of a primary electroless copper and the secondary electroless
metal gives a resulting bright, attractive uniform deposit to
the plastic substrate. ~o subsequent electroplating such as
; with electroplated copper, nicXel,,chromium, as necessary in
prior art, is further required in the present invention. And
this constitutes an important improvement over existing
'' commercial processes.
Parts of the primary electroless copper coating may
be mechanically removed prior to applying the secondary electro-
less coating (the overlayer) by immersion of the substrate in
the secondary electroless metal bath. The secondary coating
(the overlayer) is produced only in those substrate surface
areas having a primary copper underlayer.
The primary electroless copper bath is maintained
basic 11.5-13.5 pH (preferably 12.0-12.5 and the secondary
1~60C~6
electroless bath operates at pH values characteristic to the
electroless metal bath being used.
In the primary electroless coating bath (the under-
layer), solutions of copper salts in polar solvents (prefer-
ably aqueous) are employed together with a chelating agent,
an alkaline pH adjusting chemical, reducer and bath stabilizer.
The secondary electrolessly deposited metal (the overlayer)
possesses similar addition agents in the particular bath but
will vary according to which metal is being deposited.
Examples of formulations for both the primary electroless
copper and the secondary electroless overlayer metal are
given below.
~ le resultant produce is characterized by high
reflectivity and adhesion.
In accordance with a particular embodiment of the
invention, a method of electroless metal coating to produce
a bright metal of high refl~ctivity and adhesion comprises:
treating a nonconductive substrate to prepare it for electro-
less coating, then applying a primary copper underlayer to
the substrate by simultaneous reduction of a copper compound
while dissolved in an electroless bath in contact with the
substrate while chelating copper ions therein and at a rate
of ,2-,4 mils per hour, then applying a secondary metal coat-
ing to the said copper surfaced substrate by electroless
coating, the secondary solution comprising sufficient phos-
phorus and being controlled to produce 6-12 weight percent
phosphorus in the final coating produced from the secondary
coating solution.
In accordance with a Curther embodiment of the
invention, a method of electroless metal coating to produce
a bright metal of high reflectivity and adhesion comprises:
- 7 -
~".
.
360~6
treating a substrate surface to prepare it for electroless
coating, then treating the entirety of said surface with a
primary electroless copper coating solution maintained at
a basic pH of 11.5 - 13.5 and containing a copper chelating
agent, and coating the surface with copper at .2 - .4 mils
per hour, then treating the said surface with a secondary
electroless metal coating solution maintained at its
characteristic electroless coating pH, the secondary solution
comprising sufficient phosphorus and being controlled to
produce 6-12 weight percent phosphorus in the final coating
produced from the secondary coating solution.
In accordance with a still further embodiment of
the invention, a method of nickel coating comprises:
etching and activating the surface of one or more substrate
articles in a single step, acceleration treatment of the
substrate surfaces, immersing of the substrates in a primary
copper solution maintained at 25-35C and pH of 11.5-13.5
for 5-15 minutes to produce a primary copper coating thereon,
and then immersing the substrate without rinsing or neutral-
ization, into a secondary electroless metal coating solutionmaintained at temperature and pH to produce a self building
brightening of the surfaces, the secondary solution compris-
ing sufficient phosphorus and being controlled to produce
6-12 weight percent phosphorus in the final coating produced
from the secondary coating solution.
Other objects, features and advantages of the
present invention will be apparent to ihose skilled in the
art from the following detailed description of preferred
embodiments thereof.
. . ~ .
11360(~6
DETAILED DESCRIPTIO~ OF PREFERRED EMBODIMENTS
More specifically, the improved process of the
present invention is comprised of the following sequence of
steps used, for example, with acrylonitrile-butadiene
styrene (ABS) which is selected because of its excellent
platability:
(1) Surface condition or etch the ABS using the conventional
cnromic acid-sulphuric acid aqueous solution.
(2) Rinse in water.
0 ~3) ~eutralize residual etch solution in a dilute sodium
bisulfite solution.
(4) Rinse in water.
(5~ Activate in the one-stage non-noble or noble catalyst
solution.
(6) Rinse in water.
(7) Accelerate in an alkaline sodium borohydride or dilute
- 7b -
~ ~ ~ ~ 36~D ~
Ij
P02 1! fluoboric acid solution.
(8) Rinse in water,
¦¦ (9) Apply the primary electroless copper (foundation metal).
!l (10) Apply the secondary electroless metal (bright deposit).
~5 1I EXAMPLES 1-4 which follow are more specific illustra- !
I tive (non-limiting) detailed descriptions of practice of the
¦~ present invention as applied to plastic radio knobs moLded in
a platable grade of acrylonitrile-butadiene-styrene (ABS).
l All solutions and baths are aqueous.
- EXAMPLE 1
- (1) Etch the part in the conventional chromic acid-sulphuric
acid solution of the following composition:
Chromic Acid (CrO3 - 184 grams/liter
B ll Sulphuric Acid (H2S04) (66 Bè) - 368 grams/liter
Fluorad FC-95 -~1.0 ~literFluorocarbon surfactant
,~ ' , - ,
Treatment - 5 minutes at 65 - 70C~ ¦
(2) Water rinse
~3) ~eutralize
~-~ Sodium bisulfite (~a2S204 . 2 H2O - ¦
150-200 grams/liter)
Treatment - 1 minute at 25 - 30C.
(4) Water rinse
(5) Activate (non-noble catalyst~
Acidified cuprous chloride solution (CuCl-HCl)
Treatment - 15 minutes at 40C.
(6) Hot water rinse - 5 minutes
~7) Acceleration
¦ Sodium borohydride (NaBH4) - 1 gram/Liter
- - Sodium hydroxide tNaOH) - 1 ~ram/liter
Fluorad FC-95 surfactant (1% solution)- 1 ml/liter
Treatment - 10 minutes at 30C.
,
j -8-
"
. ~i360~B
(8) Water rinse -
(9) Primary ELectroless~C~pper Bath Immersion (bath composition)
Copper sulphate (~USO4 . 5H2O) 20 grams/liter
Trisodium salt of nitrilotriacetic
acid (NTA.Na3) 50 grams/liter
Sodium hydroxide (NaOH) 20 grams/liter
Sodium cyanide (NaCN) .01-.02 gramsjliter
Formaldehyde (37% by weight) 30 grams/liter
O~eratin~ Conditions
Temperature 25-30C
pH 12.0-12.5
Time 30-60 minutes
(10) Secondary Electroless Bath Immersion - to produce, for
example, nickel overlayer - (bath composition)
Nickel sulphate (NiSO4 . 6 H20) 20 grams/liter
Lactic acid (80%) (CH3CHOH COOH) 30 grams/liter
Propionic acid (CH3 r CH2 . COOH) 2 grams/liter
Lead acetate (Pb(CH3O2)2.3H2O) .001 grams/liter
Sodium hypophosphite (NaH2PO2.H2O) 25 grams/liter
Operatinq Conditions
Temperature 70-90C
pH 4.5-5.5
Time 20-30 minutes
Activation can be carried out using either a non-
noble or noble catalyst [see also step 5 of EXAMPLE 1 herein].
In EXAMPLE 1, a non-noble catalyst, using acidified cuprous
chloride solution, is shown with subsequent acceleration using
alkaline sodium borohydride. A noble catalyst may also be
used, e.g., the stannous chloride - palladium chloride colloidal
30 type catalyst, using 10% fluoboric acid as the accelerator.
il` ' ~1360~ 1
li I
02 ~ The end product comprises 6-12 weight percent of
¦,phosphorous in the overlayer because of hypophosphite reducing
¦lagent usage in the secondary electroless coating bath. The
¦lunderlayer thickness is typically .05--.15 mils and overlayer
S ¦thickness is usually substantially greater. The bright over-
¦layer has a reflectivity of 80-90% and is thicker and more
¦¦brittle andlor has a greater surface hardness than the underlayer.
I The hypophosite used may be ammonium - or alkali
¦¦metal (i.e., ~a, K, Li) - hypophosphite.
L0 l The general principles of the inven~ion exemplified in
,,, , the above example of primary and secondary electroless coating
steps are as follows:
¦ In the primary electroless copper bath, there is a
¦dissolved copper salt, a chelating agent in sufficient amount to ¦
'~ c,helate at least as much copper as is sought to be deposited at
desired deposition rates; one or more pH increasing means
~ (e.g. J a dissol~ed basic chemical such as~an ~ )or an
'' inorganic hydroxide or an amine)to establish the necessary, basic pH operating condition, a: stabilizer,(e.g., the cyanide
used above) and an active-reducing agent (e.g., the formaldehyde
used above or other reducing agents-containing double or triple
,bonds, e.g., oximes,such as glyoxime.or hydrazine). ~he
simultaneous chelation of metal ions and reduction reaction under
pH controlled and s~abilized conditions produces an extended-
¦ period of copper coat deposition in coherent (within itself)
¦ and adherent (to a substrate) form at commercially practical t
, ¦ high rates. The copper is very pure, usually 99.99% or higher
¦ and soft.
The secondary immersion bath uses a salt source of a
i 30 ¦ me~al to be coated; "exultant" chemicals known per se in the
¦ pla~ing arts (e.g., the lactic and propionic acids used above)
l to prevent powdering or other particulation of the secondary
I
11 ~o
1~ 11360
Il ' .
P02 ~Icoating; a stabilizer (e g.> the acetate)and a reducing agent
containing phosphorous or boron [which will inevitably leave
¦~traces of such elements in the secondary coating, sometimes
liaffecting the physical properties of the secondary coating --
3 ¦¦ e.g., hardening it,~ No chelation is utilized in the secondary
¦~coating. Separate brightness and pH adjusting means may also
be added if their functions are not inherently satisfied by
by the above mentioned components of the secondary bath.
The overlayer generally has a microhardness of
L0 400-600 Vickers pa~ti~ular~y when nickel and nickel alloys are
deposited and is in any case preferably thicker and more brittle.,
and/or has a higher surface hardness, than the copper underlayer
and a reflectivity of about 80-90% under standard reflectivity
i eflni~ of the plating art~.
il I
ll
. I
l . I
In the formulation given for the electroless copper
in EXAMPLE 1, the ductility of the electroless copper (the
underlayer) is excellent and the appearance of the deposit is
close-grained, smooth and semibright. Its metallurgical
properties are highly satisfactory for a foundation or under-
layer highly receptive to receive the electroless overlayer.
The rate of deposition of this electroless copper
(the underlayer) is .2 - .4 mils per hour under properly con-
trolled bath composition with continuous filtration to,insure
against rapid decomposition from particles in the bath.
Mechanical agitation is recommended and preferred over air
i agitation.
Other copper salts may be utilized as the source of
copper metal such as the nitrate, acetate or chloride salts of
copper in lieu of copper sulphate. Other chelating agents can
be used in place of NTA.Na3, e.g., PDTA.~a4 (tetrasodium salt
of propylenediamine tetraacetic acid) and EDTA (ethylenediamine
tetraacetic acid) or its tetra-sodium salt (EDTA.Na4) or
Rochelle Salts (i.e., sodium potassium tartrate) - -
(NaKC4H4o6 4~2)
, Stabilizers, other than,sodium cyanide, can be used,
e.g., thiourea or mercaptobenzothiazole. Potassium hydroxide
can be employed as the alkaline agent to replace sodium hydroxide.
There are many formulations for electroless copper
baths used in industry and known to the artisan active in the
field of metallizing plastics and printed circuitry but all
require electroplating methods for completion of the process.
, Innumerable pa'ents, technical journals and trade brochures
describe these baths and processes. The improvement set forth
in this invention is the complete elimination of the electro-
plating process over the electroless copper given in EXAMPLE 1.
The overlayer electroless nickel bath and,
- 12 -
'' ~f3
1136006
'1' , .
C P02 Il~ likewise, the other (M) overlayer coatings covered subsequently
/77 11~ in this prese~t disclosure, have self-building brightness, i.e.,
¦~ the thicker the coating, the brighter the deposit.
1, This brightness is achieved, within the scope of this
Ij invention, by utilizing commercially available proprietary
brighteners of the chemical classification used in the electro-
~! lytic baths
Following the formation of the primary electroless
copper (the underlayer~, optionally, the copper coated substrate
~10 ¦ can be dipped in a 5% (by weight) sodium cyanide solution,
I rinsed well in water, then immersed in 10% (by volume) sulphuric !
; ~ acid solution and again rinsed prior to placing the part in the
secondary electroless bath to insure a clean, active electro-
less copper surface.
¦ Besides the application of a bright secondary (M)
overlayer of copper or nickel, an adherent bright metallic
coating of silver, gold, cobalt, tin, indium, palladium,
chromium, molybdenum and alloys thereof (e.g , nickel-cobalt,
nickel-iron, nickel-molybdenum or the so-called polyalloy systems)
can be deposited and fall within the scope of this invention.
Further examples of secondary electroless overlayer
coatings, applied over the primary underlayer electroless
j copper, are herewith given:
EXAMPLE 2 -- Electroless Cobalt (Overlayer) Bath
Bath Composition:
Cobalt chloride (CoCl2 .6H20) ~ 30 grams/liter
Sodium hypophosphite (NaH2P02.H2O) 20 grams~liter
Sodium citrate (Na3C6H507.2 H2O) 35 gramslliter
Ammonium chloride (NH4Cl) 50 grams/liter
Operating conditions:
Temperature 70-90C
pH 9-10
¦ -13- !
~1 '. .
,1 ~1360a6
C P02 ~`1 Time 20-30 minutes
/77 1I Deposition rate .6 mils/hour
EXAMPLE 3 - Electroless Nickel-Cobalt Polyalloy (Overlayer) Bath'
I Bath Composition:
j Cobalt Chloride (CoC12 .6H2O)30 grams/liter
Nickel chloride (NiCl2 .6H2O)30 grams/liter
Rochelle salt (NaKC4H4O~.4H2O)200 grams/liter
Ammonium chloride (NH4Cl)50 grams/liter
Sodium hypophosphite (NaH2PO2 H2O) 20 grams/liter
10 ` Operating Conditions:
Temperature 70-90C
pH 8-lO
¦ Time 20-30 minutes
Deposition rate .6 mils/hour
EXAMPLE 4 - Electroless Gold (Overlayer) Bath
Bath Composition: ¦
Gold Chloride (AuC13.2H2O) 60 grams/liter -
Ammonium chloride (N~4Cl) 75 grams/liter
Sodium citrate (~a3C6H507.2 H2O) 50 grams/liter
Sodium hypophosphite (~a ~ PO2.H2O) 10 grams/liter
Operating Conditions:
Temperature 70-90C
pH 7-8
Time 5-10 minutes
Deposition rate .3 mil/hour
Metal salts other than those shown in the EX~PLES
2, 3, 4 formulations can be employed. For example, in lieu of
nickel sulphate, chloride, acetate, ammonium sulphate salts of
nickel can be used. Cobalt sulphate, acetate, and ammonium
chloride can replace cobalt chloride. Potassium gold cyanide salt
can be the source of metallic gold instead of gold chloride
In place of sodium hypophosphite which is the reducing 3
-14- 1
I
1, . , ` ~ .
1136006 ( '~
-!l
C P02 ¦1 agent in the formulations, dimethylamine borane (DMAB) and
/77 1~ sodium borohydride ~NasH4) can be employed. The electroless
¦I deposit would then contain boron as an alloy instead of
j phosphorus. Citric acid can be used to replace sodium citrate.
Within the scope of this invention are the various
i brightenèrs utilized in these so-called secondary electroless
baths In EXAMPLES 1-4, commercial or proprietary brighteners
are used to achieve the desired brightness. Heretofore these
brighteners were only employed in any commercially significant
I way as far as is known in connection with electrolytic baths and ¦
, ~ ~ not in connection with electroless baths such as those
¦~ exemplif ed ln this disclo~ure. In EXAMPLES L, 2 and, wherein
¦l electroless deposits of nickel, cobalt, and the nickel-cobalt
polyalloy were applied to the electroless copper (the underlayer)¦
I certain carefully selected brighteners normally used for electro-¦
I ¦ lytic nLckel plating worked highly satisfactorily under properly
controlled conditions; for example> brightener concentration, I
bath ingredient composition, temperature and pH These : `¦
brighteners are of the first and second class well-known to the
artisan.
The first class (=C - SO2 - ) brighteners consist of
sulfonic acids, sulfonates, sulfonamides, sulfonimides, etc.
linked chemically with naphthalene, benzene, toluene, naphthyla-
mine, etc. The second class of brighteners contain metal ions
¦ such as selenium, cadmium, sulphur, thioureas, etc.
s ¦ I have found that p-toluene-sulfamide or sodium
¦ benzene disulfonate as a first class brightener and cadmium
sulfate as a second class brightener,in concentrations in the
range of .5 - 2.0 grams per liter, worked well in the secondary
electroless baths of nickel, cobalt and nickel-cobalt polyalloy.
Likewise, o-benzoyl sulfimide and p-amino phenol as first class
brighteners and cadmium sulfate, lead acetate and sodium thiosul-
~; l l
11 i
` I ~136006
'I '.
. P02 ¦fate as second class addition agents brought about brightness
~77 jespecially in the cobalt and nickel-cobalt alloy electroless baths. !
. ~ I The electroless gold bath electrolessly plated
brightly using tetraethylene pentamines and triethylamine in
~ 5 concentrations of 1-2 grams per liter as single brighteners.
! ~ ~ Many of the aforementioned brighteners which, as
~reviously stated~ are usually recommended only for electrolytic
plating solutions.
~ It is important to again stress that the primary electro
0 ` ess copper (the underlayer) and the secondary electroless bath
the overlayer) shown in EXAMPLES l, 2, 3, 4 must be employed
ointly for the best practice of this invention. Likewise, it
s important to point out that the improvement over existing
~ ommercial processes lies in the fact that no subsequent electro-
L5 lating of the electroless film is necessary when this dual
lectroless system is used.
Furthermore, within the scope of this inve~tion, is
m important industrial process of selective electroless coating
nade possible only by utilization of the process disclosed above.
I An automotive radio knob, for example, molded out
~f black ABS material is electrolessly coated with the primary
~lectroléss copper described above. The center section of this
~ ow is machined on a wood turning lathe or similar equipment
x ¦(e.g., on a miller, shaper, grinder, etc.) to remove the relatively
~hin layer of this ductile, machinable primary copper from the
~enter section of the knob to expose the original black plastic
ubstrate. The part then receives the bright secondary electro-
Less metal by immersion in the electroless bath to produce the
- ~esired metal, The net result is a bright automotive knob
~etallized all over with the bright metal except at the center
~section where the originally mol'ded black ABS plastic is exposed
~: ~n other words, an attractive combination of metal and plastic is chieved. -16-
'': I
6(~06 ( i
,.,' 11 '
; P02 ¦I The intermediate machining step obliterates surface
7 I activation history in the treated area so that no secondary
metal adheres to the mechanically treated portion. No finishing
steps are necessary other than rinsing in water. ~ -
I Prior methods employed to accomplish selective
~¦metallizing required the use of costly spray masks or stencils in
conjunction with stop off paints or inks or silk screen or
photographic procedures as used in printed circuitry, hot
stamping, adhesive-backed inserts, two-shot molding, etc.
) ¦ Furthermore, since the disclosed process is a totally
electroless method requiring no subsequent electroplating,
costly complex racking for electrical connection is totally
eliminated. Hence, the net result is a low cost selective
plating process.
Other applications for selectively decorating plastic
items for the novelty field include selective plating of
jewelry items, buttons, placques, etc. A variety of geometric
designs are now available. In mass production, automatic
cutting machines can be adapted economically to remove the
¦primary electroless copper in the predetermined areas prior to
the application of the bright secondary metal.
¦ Although the invention has been described and illus-
trated in detail, it is clearly understood that the same is by
way of illustration and example only and is not taken by way
of limitation, the spirit and scope of this invention being
limited ly by ~he terms of the appended claims which follow.
~:'
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I -17-
